1. Technical Field
The invention relates to data communication networks. More particularly, the invention relates to transmitting information from a faster network to a data terminal via a slow network connection.
2. Description of the Prior Art
Electronic commercial and academic computer networks have been in existence for many years. An example of a commercial network is America On-Line. The largest and best-known electronic network is commonly known as the Internet. The Internet is a world-wide “network of networks” that is composed of thousands of interconnected computers and computer networks.
The preferred protocol of communications on the Internet is a set of standards and protocols, commonly referred to as TCP/IP. These TCP/IP protocols provide the means to establish a connection between two nodes on the network, and to subsequently transfer messages and data between these nodes. TCP (Transmission Control Protocol) provides the logical connection to ensure delivery of an entire message or file, while IP (Internet Protocol) provides the routing mechanism.
The majority of residential and commercial users of such computer networks (the clients) do not have a direct connection to the network. They subscribe to the services of an access provider, commonly called “Internet Service Provider” (ISP) in the case of the Internet. Clients use a personal computer or other terminal that is equipped with a data modem, to dial into the ISP connection service.
FIG. 1 is a diagram of the topology of an Internet connection via an ISP, according to the prior art. The ISP maintains a network 10 that connects its clients to the Internet 26. This network includes the ISP backbone 12, which is an internal set of connected nodes. ISP backbones are typically connected to points of presence, known as POPs 14, and management (control) centers 16. The POP is typically the local exchange that users dial into via modem. There are usually few management centers and many POPs in an ISP backbone.
The ISP typically connects to the Internet via a Local Area Network (LAN) 28 at the management center. However, the ISP host may also be connected to the Internet via a Wide Area Network (WAN) such as the X.25 style Public Data Network (PDN). The LAN communicates with the Internet 26 through a physical, wide-bandwidth connection 30. However, the client does not connect to the LAN through such wide-bandwidth connection. Rather, the client accesses the Internet by using a computer 18 with a modem 20 to dial up, through the public telephone system 22, another modem in a local POP 24. This modem-to-modem connection is a relatively slow, low bandwidth two-directional link.
The ISP usually provides a relatively slow point-to-point (serial) two-dimensional link, through which the client communicates directly to the Internet, using the Internet standard TCP/IP protocols. Such serial link transfers digital data-one bit after the other. The Recommended Standard-232 (RS-232) is the standard commonly followed for serial data transmission. (See, for example, Electronic Industries Association, EIA Standard RS-232-C, “Interface Between Data Terminal Equipment and Data Communications Equipment Employing Serial Binary Data Interchange”, August 1969.)
Point-to-point links are among the oldest methods of data communications and almost every host supports point-to-point connections. A long-distance point-to-point link is achieved by using a modem to establish a dial-up link between a display terminal, such as a personal computer, and the other host, such as a host located on the ISP site.
The communication over the serial point-to-point line is in the form of encapsulated (framed) TCP/IP datagrams (data packets) using either Serial Line Internet Protocol (SLIP) or Point-to-Point protocol (PPP) packet framing.
The SLIP protocol is described in IETF Network Working Group (J. Romkey), “A NONSTANDARD FOR TRANSMISSION OF IP DATAGRAMS OVER SERIAL LINES: SLIP,” Request for Comments: 1055-June 1988. The PPP protocol is described in IETF Network Working Group (D. Perkins), “The Point-to-Point Protocol for the Transmission of Multi-Protocol Datagrams Over Point-to-Point Links,” Request for Comments: 1171. SLIP transmits IP data packets over any serial link, such as a telephone line. It is generally used to provide Internet access to networks that support TCP/IP. PPP is a more common data link protocol that provides dial-up access over serial lines.
FIG. 2 is a diagram of a traditional Internet connection according to the prior art. To communicate on the Internet 26, an appliance or terminal (the client) 18 establishes a logical connection with a content provider. This connection is typically made using dial-up equipment, such as a modem 46 to connect to the public telephone system 22. The information transmitted over the telephone line is composed of PPP-wrapped TCP/IP data packets. Essentially, the ISP 10 is a transparent channel through which the client directly communicates with content providers, such as Web sites 51.
There are several disadvantages to this prior art approach. One major disadvantage is that of cost and complexity. Each terminal must be equipped with the ability to handle TCP/IP and PPP or SLIP protocols. This can require as much as 90 Kbytes of code and 70 Kbytes of data. Another major disadvantage is that of bandwidth. The Internet protocol overhead must be transmitted through the slow serial link, thereby reducing the actual useful bandwidth.
Yet another disadvantage is the need to duplicate, in each terminal, the code to deal with every possible type of data that may be transferred. Additionally, the established connection between the client and the Web server is recreated for every required file. This prevents a more general solution where commonly fetched files or messages are cached.
The World-Wide Web (Web) is an Internet client-server distributed information retrieval system. On the Web documents, menus, and indices are represented to the user as hypertext objects. Hypertext is a collection of documents containing cross-references or “links”. These links enable the user, with the aid of an interactive browser program, to move from one document to another.
The Web may be accessed through other types of devices than a computer, including personal data assistants, fax machines, and Internet-capable telephones. One device that can provide Internet access is the terminal described in M. Valentaten, B. Moeschen, Y. Friedman, Y.-T. Sidi, Z. Blkowsky, Z. Peleg, Multi-Mode Home Terminal System that Utilizes a Single Embedded General Purpose/DSP Processor and a Single Random Access Memory, U.S. Pat. No. 5,259,940 (Oct. 5, 1993).
An internet access device, such as a modem-connected personal computer, generally uses a software application known as a Web browser to access the Web information available on the Internet. Such Web browsers, including Navigator, manufactured by Netscape Communications Corporation of Mountain View, Calif., and Mosaic, owned by the National Center for Supercomputing Applications (NCSA) at the University of Illinois, Urbana-Champaign, use a direct connection to the Web over SLIP/PPP. Thus, all of the overhead, in particular the parallel protocol overhead, is over the slow link.
To mitigate the above-mentioned disadvantages, prior art solutions that do not require the display terminal to handle the TCP/IP protocol set have been used to access the Internet. One such solution is for the user to acquire a shell account on the ISP host computer. With a shell account, a simple text transfer protocol and a terminal-emulator program are used to permit the user to communicate with the Internet through the display terminal, using a text-only Web browser program. One such text-only Web browser is Lynx, developed by the University of Kansas and currently maintained by Foteos Macrides at the Worcester Foundation for Biological Research. However, the shell account approach is subject to the major disadvantage that only plain-text information, and not images, colors, and sounds can be viewed.
Another prior art approach is that of the commercial Internet Web browser SlipKnot, developed by MicroMind, Inc. SlipKnot permits Web browsing through a serial link to a server, typically a Unix server, using a simple dial-in program. A TCP/IP stack is not required. When a user selects a hyperlink using SlipKnot, a textual description of the hyperlink is transferred to the ISP. SlipKnot uses the capabilities of the shell account to execute an “agent” program (such as Lynx) on the ISP machine. This agent fetches the requested multimedia file and uses a data-transfer program, such as xmodem, to transfer the file to the display terminal for display.
However, SlipKnot can be inconvenient to use and install. Furthermore, because the agent program is invoked separately for each separate request, information transfer is inefficient and slow. The SlipKnot method can handle only one request at a time and allows only local caching on the client.
It would therefore be an advantage to provide a method and system that improves the transfer of information from a faster network to a data terminal via a low-bandwidth link. It would be a further advantage if such method and system filters irrelevant Internet information prior to its transfer over the low-bandwidth link. It would be yet another advantage if such method and system reduces, if not entirely eliminates, protocol negotiation over the low-bandwidth link.